1. Field of the Invention
The present invention relates to a vibration damping device to be used, for example, as engine mounts, body mounts, sub-frame mounts and the like on motor vehicles as well as to a mounting member for a vibration damping device constituting such device.
2. Description of the Related Art
Conventionally, there has been known a vibration damping device such as the one described in U.S. Pat. No. 5,964,456 as a kind of vibration damping coupling body or a vibration damping supporting body interposed between the members constituting a vibration transmission system. The vibration damping device has the structure where a first mounting member and a second mounting member are elastically connected by a main rubber elastic body.
Meanwhile, a bracket is attached to the first mounting member of the vibration damping device. The vibration damping device described in U.S. Pat. No. 5,964,456 has the first mounting member and the bracket overlaid and fixed on top of each other by a bolt.
However, since the structure described in U.S. Pat. No. 5,964,456 requires a fixing bolt to fix the first mounting member to the bracket, the number of parts is increased, posing a problem of structural complication, and at the same time, it requires to use a comparatively large fixing bolt to firmly fix the first mounting member to the bracket, which is likely to pose a problem of increased weight. Also, attaching the fixing bolt requires multiple rounds of screwing operations, which is cumbersome and time consuming, while posing another problem of difficulties in controlling the fixing power by the magnitude of tightening torque of the fixing bolt.
Japanese Unexamined Patent Publication No. JP-A-2010-048281 adopts the structure where a bracket is press-fitted in a first mounting member in a cylindrical shape covered with a rubber sheath layer along the inner peripheral surface. However, since the first mounting member in a cylindrical shape is formed by pressing a metal plate, the upper portion where the bracket is inserted into and the lower portion where the main rubber elastic body is fixed are made integrally, the upper and lower portions restrict the shapes of each other, posing a problem of lower degree of design freedom. That is, the first mounting member has the shape and size of its upper portion set in accordance with those of the bracket, whereas the shape and size of its lower portion is favorably set in accordance with the vibration damping properties and the like. However, in the structure where the upper and lower portions are integrally made, once the shape of the upper portion is determined in line with the bracket, it was difficult to freely design the shape of the lower portion to maximize the vibration damping performance since the shape of the lower portion is limited to the one moldable by press work corresponding to the upper portion. In addition, the amount of protrusion of the lower portion beyond the upper portion is limited to the range moldable by pressing a metal plate, which posed a risk of difficulties in fully meeting the need for a larger protrusion.
Also, Japanese Unexamined Patent Publication No. JP-A-2013-108522 proposes a structure where the bracket is connected to the mounting member as if being embraced by it, by means of bending the plate portion (25) of the first mounting member (the second mounting fitting 5 in JP-A-2013-108522) along the surface of the bracket. However, according to this structure of JP-A-2013-108522, the bolt that fixes the first mounting member to the bracket is no longer needed, whereas there was an inevitable problem of increased size of the joint portion between the first mounting member and the bracket. In addition, by providing a large plate bent to embrace the outside of the bracket, there was a potential problem of increased size of the first mounting member itself.
Therefore, it was hard to say that any of the structures described in JP-A-2010-048281 and JP-A-2013-108522 was good for the first mounting member, which means that there was a room for improvement.